Performance Of Double-reheat Coal-fired Power System Aided With Solar And Carbon Capture Systems

At present,by realizing the replacement of clean energy and improving the utilization efficiency of energy,it is a new idea to realize carbon capture and reduce CO₂emission in thermal power plants.Based on a 660MW double reheat unit,this paper establishes three coupled scenarios of solar power-double reheat coal-fired units based on carbon capture.The first scenario is to replace the No.1 high-pressure heater with a solar energy system,and by exhausting the steam extraction to get higher thermal efficiency.The scenario II is to use the solar energy system to supply the saturated water to the main feedwater pipeline,and the bled steam from the intermediate-pressure cylinder supplies heat to the reboiler of carbon capture system.In scenario III,the required heat is supplied by both the intermediate-pressure cylinder and solar energy system.The opening degree of the valves,that is,the ratio of the energy from the solar system to the intermediate-pressure cylinder,is flexibly regulated during operation according to local meteorological conditions and energy demands.The matrix models of thermodynamic analysis,exergy analysis and contribution analysis of fuel exergy are established,and the important indicators including the thermal economy index,exergy analysis index,average carbon capture cost,power generation cost and external fuel exergy contribution of each system,are evaluated.The results indicate that all three scenarios can improve the thermal performance of the system,by comparing each performance index,the second scenario that the solar collector system replaces the first high-pressure heater and the heat source of reboiler extracts from the intermediate pressure cylinder,is the best integration scheme.However,the thermoeconomic indicators in scenario II including coal consumption rate,power generation efficiency and cycle thermal efficiency are less competitive than those in scenario III,and exergy losses in boiler and heat regenerative system are also higher than scenario III.But compared with scenario III,the economy of scenario II is superior and the potential of investment and utilization is more competitive.The parameter sensitivity analysis for scenario II shows that the increase of carbon capture rate or renewable energy consumption results in the raising of coal consumption and the reduction of cycle thermal efficiency and power generation efficiency.In addition,for 1%increase in the carbon capture rate,the turbine exergy losses are reduced by 4.424kJ/kg and the exergy efficiency is increased by 0.1%.With the increase of solar radiation intensity,both the average carbon capture cost of the system and contribution of solar exergy diminish gradually,whereas the contributions of coal exergy in boiler,primary reheat and double reheat systems promote gradually.When optimizing scenario III,under the ratio of the heat from solar system to that required by reboiler of?=0.3,the coupled system presents better thermal performance and reasonable irreversible degree.Under the aim of energy conservation and emission reduction,scenario III of?=0.3 is conducive to the investment and economic benefits.